Many industries encounter a problem with particulate matter suspended in a gas, such as air. In some situations, the particulate matter is a valuable product to be recovered. In other situations, the particulate matter is simply a pollutant to be removed prior to discharge or recirculation.
Systems for cleaning an air or gas stream laden with particular matter include air filter assemblies that have filter elements situated in a housing. The filter element may be a bag made of suitable fabric or a rigid media such as pleated paper. Cleaning of the filter element(s) may be accomplished by periodically pulsing a brief jet of pressurized air in a reverse flow through the filter element. Such air filter assemblies are disclosed in, for example, U.S. Pat. No. 6,090,173 (Johnson, et al.) and U.S. Pat. No. 5,562,746 (Raether).
Several challenges are inherent in designing such a device. First, the reverse flow cleaning system must not overly interfere with or compromise the forward flow of air through the filter media such that maximum efficiency may be achieved. Second, the pulse of reverse flow air needs to affect cleaning of substantially the entire length of the filter media, as evenly as possible, in order to again maximize efficiency of the air filtration process and the filter media cleaning process. Third, it is desirable to design the reverse flow pulse delivery system to operate as efficiently as possible while (effective with low energy input) achieving the first two goals.
Prior art systems have used a venturi at the air flow exit of a tubular filter element in order to recover some of the high pressure drop (or pressure differential) that occurs between dirty air and clean air chambers in the system. Pulse-jet cleaning systems utilize very short bursts of very high velocity (supersonic) air which results in the generation of significant noise as the reverse flow cleaning system is operated. The present invention provides the combination of a venturi design, blowpipe nozzle, and selected spacing therebetween in order to maximize the cleaning effect on the filter media.